1. Field of Invention
The present invention relates to a magnetic disc drive motor for rotationally driving magnetic discs carried on it.
2. Background Prior Art
Known magnetic disc drive motors to be used for magnetic disc memory devices normally have a configuration as described below.
As illustrated in FIG. 3, motor frame 1 is provided on its central area with a substantially cylindrical holder 2, which holder 2 rotatably holds in it a shaft 4 by way of ball bearings 3, 3. A hollow and cylindrical hub 5 is rigidly fitted to the shaft 4, the hub 5 carries a number of magnetic discs 6 on its outer periphery arranged in rows and rigidly fitted thereto. The hub 5 also carries a drive magnet 7 on its inner periphery rigidly fitted thereto.
On the other hand, the holder 2 carries, on its outer periphery, a stator core 8 rigidly fitted thereto and surrounded by a coil 9 wound around it. The coil 9 and the drive magnet 7 are arranged in juxtaposition. The hub 5 and, therefore, the magnetic discs 6 on it are rotated when the coil 9 is energized.
A magnetic disc drive motor having a configuration as described above is required to be manufactured to provide high precision in terms of revolving oscillation and external vibrations. Furthermore, vibration of the motor itself should be minimized. Any vibration caused by the rotation of the motor can result in unreproducible oscillation of the magnetic disc that hinders normal data reading operation.
Conventionally, the problem of vibration is eliminated by providing a motor frame 1 having a thickness greater than a threshold value in order to enhance the rigidity of the motor frame 1 in order to minimize generation of unreproducible oscillation. If the motor frame 1 has a low rigidity, generation of unreproducible oscillation will be remarkable as the motor frame 1 and the ball bearings 3 can exhibit resonated vibration.
The demand for reduction of size and thickness observed in recent years, however, makes it difficult to realize a motor frame 1 having a large frame thickness within the very limited space allowed for providing a miniaturized memory device. Furthermore, the use of a highly rigid material for the motor frame 1 can considerably raise the overall cost of such a device.
Therefore, it is an object of the present invention to provide a small magnetic disc drive motor having a simple configuration and a highly rigid motor frame that provides a stable rotary drive operation of magnetic discs.